Light receiving element, ranging module, and electronic apparatus

ABSTRACT

Disclosed is a light receiving element including an on-chip lens, a wiring layer, and a semiconductor layer disposed between the on-chip lens and the wiring layer. The semiconductor layer includes a photodiode, a first transfer transistor that transfers electric charge generated in the photodiode to a first charge storage portion, a second transfer transistor that transfers electric charge generated in the photodiode to a second charge storage portion, and an interpixel separation portion that separates the semiconductor layers of adjacent pixels from each other, for at least part of the semiconductor layer in the depth direction. The wiring layer has at least one layer including a light blocking member. The light blocking member is disposed to overlap with the photodiode in a plan view.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/878,486, filed May 19, 2020, which is a continuation of U.S. patentapplication Ser. No. 16/504,961 filed Jul. 8, 2019, which claims thebenefit of Japanese Priority Patent Application JP 2018-135395 filed onJul. 18, 2018, the entire disclosures of each of which are incorporatedherein by reference.

TECHNICAL FIELD

The present technology relates to a light receiving element, a rangingmodule, and an electronic apparatus, and more particularly, to a lightreceiving element, a ranging module, and an electronic apparatus thatare designed to be capable of improving characteristics.

BACKGROUND ART

Ranging systems using an indirect time of flight (ToF) method have beenknown. In such a ranging system, signal charges obtained by receivingreflected light of active light that is emitted from a light emittingdiode (LED) or a laser at a certain phase and is reflected by an objectare distributed to different regions at high speed. Therefore, a sensorcapable of the distribution is necessary.

In view of this, a technology has been suggested for enabling high-speedmodulation of a wide region in a substrate of a sensor by applyingvoltage directly to the substrate and thus generating electric currentin the substrate, for example (see PTL 1, for example). Such a sensor isalso called a current assisted photonic demodulator (CAPD) sensor.

CITATION LIST Patent Literature

[PTL 1]

JP 2011-86904 A

SUMMARY Technical Problem

However, it is difficult to obtain a CAPD sensor with sufficientcharacteristics by the above described technology.

For example, the above described CAPD sensor is a surface-illuminatedsensor in which wiring lines and the like are disposed on the surface ofthe substrate on the side on which light from outside is received.

To secure the photoelectric conversion region, it is desirable thatthere is no wiring line or the like that blocks the light path ofincident light on the light receiving surface side of a photodiode (PD)or a photoelectric conversion portion. In a surface-illuminated CAPDsensor, however, wiring lines for extracting charges, various kinds ofcontrol lines, and signal lines are disposed on the light receivingsurface side of a PD, depending on the structure. As a result, thephotoelectric conversion region is limited. That is, it is difficult tosecure a sufficient photoelectric conversion region, and characteristicssuch as the pixel sensitivity might be degraded.

Further, in a case where a CAPD sensor is used in a place subjected toexternal light, the external light component becomes a noise componentin the indirect ToF method in which ranging is performed with activelight. Therefore, to secure a sufficient signal-to-noise ratio (SNratio) and obtain distance information, it is necessary to secure asufficient saturation signal amount (Qs). In a surface-illuminated CAPDsensor, however, there is a limitation on the wiring layout, andtherefore, it is necessary to take a measure to use a technique notinvolving a wiring capacitor, such as providing an additional transistorfor securing capacitance.

In many cases, near-infrared light of a wavelength of about 940 nm,which corresponds to a window of sunlight, is used as the light source.Near-infrared light has low quantum efficiency because the absorptioncoefficient of the silicon forming a semiconductor layer is low.

Therefore, it is necessary to increase the thickness of the siliconforming the photoelectric conversion region. In a case where the siliconis thick, charges subjected to photoelectric conversion take a long timeto reach the electrode for attracting the charges. After thedistribution is switched, some charges reach the electrode in somecases, resulting in an erroneous signal. As a result, the rangingaccuracy might become lower. In other words, the characteristics of thesensor might be degraded.

The present technology has been made in view of those circumstances, andis to enable improvement in the characteristics of a ToF sensor.

Solution to Problem

A light receiving element according to a first aspect of the presenttechnology includes:

an on-chip lens;

a wiring layer; and

a semiconductor layer disposed between the on-chip lens and the wiringlayer,

in which the semiconductor layer includes:

a photodiode;

a first transfer transistor that transfers electric charge generated inthe photodiode to a first charge storage portion;

a second transfer transistor that transfers electric charge generated inthe photodiode to a second charge storage portion; and

an interpixel separation portion that separates the semiconductor layersof adjacent pixels from each other, for at least part of thesemiconductor layer in the depth direction,

the wiring layer has at least one layer including a light blockingmember, and

the light blocking member is disposed to overlap with the photodiode ina plan view.

In the first aspect of the present technology, an on-chip lens, a wiringlayer, and a semiconductor layer disposed between the on-chip lens andthe wiring layer are provided. The semiconductor layer includes: aphotodiode; a first transfer transistor that transfers electric chargegenerated in the photodiode to a first charge storage portion; a secondtransfer transistor that transfers electric charge generated in thephotodiode to a second charge storage portion; and an interpixelseparation portion that separates the semiconductor layers of adjacentpixels from each other, for at least part of the semiconductor layer inthe depth direction. The wiring layer includes at least one layerincluding a light blocking member, and the light blocking member isprovided to overlap with the photodiode in a plan view.

A ranging module according to a second aspect of the present technologyincludes:

a light receiving member;

a light source that emits irradiation light having periodically varyingbrightness; and

a light emission controller that controls timing to emit the irradiationlight,

in which the light receiving element includes: an on-chip lens;

a wiring layer; and

a semiconductor layer disposed between the on-chip lens and the wiringlayer,

the semiconductor layer includes:

a photodiode;

a first transfer transistor that transfers electric charge generated inthe photodiode to a first charge storage portion;

a second transfer transistor that transfers electric charge generated inthe photodiode to a second charge storage portion; and

an interpixel separation portion that separates the semiconductor layersof adjacent pixels from each other, for at least part of thesemiconductor layer in the depth direction,

the wiring layer has at least one layer including a light blockingmember, and

the light blocking member is disposed to overlap with the photodiode ina plan view.

In the second aspect of the present technology, a light receivingelement, a light source that emits irradiation light having periodicallyvarying brightness, and a light emission controller that controls thetiming to emit the irradiation light are provided. In the lightreceiving element, an on-chip lens, a wiring layer, and a semiconductorlayer disposed between the on-chip lens and the wiring layer areprovided. The semiconductor layer includes: a photodiode; a firsttransfer transistor that transfers electric charge generated in thephotodiode to a first charge storage portion; a second transfertransistor that transfers electric charge generated in the photodiode toa second charge storage portion; and an interpixel separation portionthat separates the semiconductor layers of adjacent pixels from eachother, for at least part of the semiconductor layer in the depthdirection. The wiring layer includes at least one layer including alight blocking member, and the light blocking member is provided tooverlap with the photodiode in a plan view.

An electronic apparatus according to a third aspect of the presenttechnology includes:

a ranging module including:

a light receiving member;

a light source that emits irradiation light having periodically varyingbrightness; and

a light emission controller that controls timing to emit the irradiationlight,

in which the light receiving element includes:

an on-chip lens;

a wiring layer; and

a semiconductor layer disposed between the on-chip lens and the wiringlayer,

the semiconductor layer includes:

a photodiode;

a first transfer transistor that transfers electric charge generated inthe photodiode to a first charge storage portion;

a second transfer transistor that transfers electric charge generated inthe photodiode to a second charge storage portion; and

an interpixel separation portion that separates the semiconductor layersof adjacent pixels from each other, for at least part of thesemiconductor layer in the depth direction,

the wiring layer has at least one layer including a light blockingmember, and

the light blocking member is disposed to overlap with the photodiode ina plan view.

In the third aspect of the present technology, a ranging moduleincluding a light receiving element, a light source that emitsirradiation light having periodically varying brightness, and a lightemission controller that controls the timing to emit the irradiationlight is provided. In the light receiving element, an on-chip lens, awiring layer, and a semiconductor layer disposed between the on-chiplens and the wiring layer are provided. The semiconductor layerincludes: a photodiode; a first transfer transistor that transferselectric charge generated in the photodiode to a first charge storageportion; a second transfer transistor that transfers electric chargegenerated in the photodiode to a second charge storage portion; and aninterpixel separation portion that separates the semiconductor layers ofadjacent pixels from each other, for at least part of the semiconductorlayer in the depth direction. The wiring layer includes at least onelayer including a light blocking member, and the light blocking memberis provided to overlap with the photodiode in a plan view.

Advantageous Effects of Invention

According to the first through third aspects of the present technology,characteristics can be improved. Note that the effects of the presenttechnology are not limited to the effects described herein, and mayinclude any of the effects described in the present disclosure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram schematically showing an example configurationof a light receiving element to which an embodiment of the presenttechnology is applied.

FIG. 2 is a cross-sectional view showing a first example configurationof pixels.

FIG. 3 is a diagram showing an example circuit configuration of eachpixel shown in FIG. 2.

FIG. 4 is a plan view showing an example of arrangement in the pixelcircuit shown in FIG. 3.

FIG. 5 is a diagram showing another example circuit configuration ofeach pixel shown in FIG. 2.

FIG. 6 is a plan view showing an example of arrangement in the pixelcircuit shown in FIG. 5.

FIG. 7 is a diagram for explaining the effects of a back-illuminatedtype.

FIG. 8 is a diagram for explaining the effects of a back-illuminatedtype.

FIG. 9 is a diagram for explaining the effects of a back-illuminatedtype.

FIG. 10 is a diagram for explaining the effects of a back-illuminatedtype.

FIG. 11 is a diagram for explaining the effects of a back-illuminatedtype.

FIG. 12 is a cross-sectional view showing a second example configurationof pixels.

FIG. 13 is a cross-sectional view showing a third example configurationof pixels.

FIG. 14 is a cross-sectional view showing a fourth example configurationof pixels.

FIG. 15 is a cross-sectional view showing a fifth example configurationof pixels.

FIGS. 16A and 16B are perspective views showing an example configurationof a moth-eye structure.

FIGS. 17A and 17B are perspective views showing another exampleconfiguration of a moth-eye structure.

FIGS. 18A and 18B are perspective views showing other exampleconfigurations of a moth-eye structure.

FIG. 19 is a cross-sectional view showing a sixth example configurationof pixels.

FIGS. 20A through 20F are diagrams for explaining a manufacturing methodin the sixth example configuration.

FIG. 21 is a diagram showing an example of a four-tap pixelconfiguration.

FIG. 22 is a block diagram showing an example configuration of a rangingmodule to which an embodiment of the present technology is applied.

FIG. 23 is a block diagram showing an example configuration of asmartphone as an electronic apparatus to which an embodiment of thepresent technology is applied.

FIG. 24 is a block diagram schematically showing an exampleconfiguration of a vehicle control system.

FIG. 25 is an explanatory diagram showing an example of installationpositions of external information detectors and imaging units.

DESCRIPTION OF EMBODIMENTS

The following is descriptions of modes (hereinafter referred to asembodiments) for carrying out the present technology. Note thatexplanation will be made in the following order.

1. Example configuration of a light receiving element

2. Cross-sectional view of a first example configuration of pixels

3. Example circuit configuration of a pixel

4. Plan view of a pixel

5. Another example circuit configuration of a pixel

6. Plan view of a pixel

7. Effects of a back-illuminated type

8. Cross-sectional view of a second example configuration of pixels

9. Cross-sectional view of a third example configuration of pixels

10. Cross-sectional view of a fourth example configuration of pixels

11. Cross-sectional view of a fifth example configuration of pixels

12. Cross-sectional view of a sixth example configuration of pixels

13. Example of a four-tap pixel configuration

14. Example configuration of a ranging module

15. Example configuration of an electronic apparatus

16. Example applications to moving objects

<1. Example Configuration of a Light Receiving Element]

FIG. 1 is a block diagram schematically showing an example configurationof a light receiving element to which the present technology is applied.

A light receiving element 1 shown in FIG. 1 is an element that outputsranging information according to the indirect ToF method.

The light receiving element 1 receives light (reflected light) that islight (irradiation light) emitted from a predetermined light source hasbeen incident on and then reflected by an object, and outputs a depthimage in which information indicating the distance to the object isstored as a depth value. Note that the irradiation light emitted fromthe light source is infrared light having a wavelength of 780 nm to 1000nm, for example, and is pulse light that repeatedly turns on and off atpredetermined intervals.

The light receiving element 1 includes a pixel array unit 21 formed on asemiconductor substrate (not shown), and a peripheral circuit unitintegrated on the same semiconductor substrate as the pixel array unit21. The peripheral circuit unit is formed with a vertical drive unit 22,a column processing unit 23, a horizontal drive unit 24, and a systemcontrol unit 25, for example.

The light receiving element 1 further includes a signal processing unit26 and a data storage unit 27. Note that the signal processing unit 26and the data storage unit 27 may be mounted on the same substrate as thelight receiving element 1, or may be disposed on a substrate in a moduledifferent from the light receiving element 1.

The pixel array unit 21 generates charges corresponding to the amount ofreceived light, and pixels 10 that output signals corresponding to thecharges are two-dimensionally arranged in the row direction and thecolumn direction in a matrix fashion. In other words, the pixel arrayunit 21 has a plurality of pixels 10 that photoelectrically convertincident light, and output signals corresponding to the resultantcharges. The pixel 10 will be described later in detail, with referenceto FIG. 2 and the subsequent drawings.

Here, the row direction refers to the array direction of the pixels 10in the horizontal direction, and the column direction refers to thearray direction of the pixels 10 in the vertical direction. The rowdirection is the lateral direction in the drawing, and the columndirection is the longitudinal direction in the drawing.

In the matrix-like pixel array of the pixel array unit 21, pixel drivelines 28 are arranged in the row direction for the respective pixelrows, and two vertical signal lines 29 are arranged in the columndirection for each pixel column. For example, the pixel drive lines 28transmit drive signals for performing driving when signals are read fromthe pixels 10. Note that, in FIG. 1, each pixel drive line 28 is shownas one wiring line, but is not necessarily one wiring line. One end ofeach of the pixel drive lines 28 is connected to the output end of thevertical drive unit 22 corresponding to the respective rows.

The vertical drive unit 22 is formed with a shift register, an addressdecoder, and the like, and drives the respective pixels 10 in the pixelarray unit 21 collectively or row by row, for example. In other words,the vertical drive unit 22, together with the system control unit 25that controls the vertical drive unit 22, forms a drive unit thatcontrols operations of the respective pixels 10 in the pixel array unit21. Detection signals output from the respective pixels 10 in the pixelrow according to the drive control performed by the vertical drive unit22 are input to the column processing unit 23 through the verticalsignal lines 29 The column processing unit 23 performs predeterminedsignal processing on the detection signals output from the respectivepixels 10 through the vertical signal lines 29, and temporarily storesthe detection signals subjected to the signal processing. Specifically,the column processing unit 23 performs a noise removal process, ananalog-to-digital (AD) conversion process, and the like as the signalprocessing.

The horizontal drive unit 24 is formed with a shift register, an addressdecoder, and the like, and sequentially selects the unit circuitscorresponding to the pixel columns of the column processing unit 23.Through this selective scanning performed by the horizontal drive unit24, the detection signals subjected to the signal processing by thecolumn processing unit 23 for the respective unit circuits aresequentially output. The system control unit 25 includes a timinggenerator that generates various timing signals, and performs drivecontrol on the vertical drive unit 22, the column processing unit 23,the horizontal drive unit 24, and the like, on the basis of the varioustiming signals generated by the timing generator.

The signal processing unit 26 has at least an arithmetic processingfunction, and performs various kinds of signal processing such asarithmetic processing, on the basis of the detection signals that areoutput from the column processing unit 23. The data storage unit 27temporarily stores the data necessary for the signal processing to beperformed by the signal processing unit 26.

The light receiving element 1 configured as described above outputs adepth image in which information indicating the distance to the objectis stored as a depth value in a pixel value. The light receiving element1 is mounted on a vehicle, for example, and may be mounted on anin-vehicle system that measures the distance to an object outside thevehicle, a gesture recognition device that measures the distance to anobject such as the user's hand and recognizes a gesture of the user fromthe result of the measurement, or the like.

<2. Cross-Sectional View of a First Example Configuration of Pixels>

FIG. 2 is a cross-sectional view showing a first example configurationof the pixels 10 arranged in the pixel array unit 21.

The light receiving element 1 includes a semiconductor substrate 41 anda multilayer wiring layer 42 formed on the front surface side (the lowerside in the drawing). The semiconductor substrate 41 is formed withsilicon (Si), for example, and has a thickness of 1 to 6 μm, forexample. In the semiconductor substrate 41, N-type (a secondconductivity type) semiconductor regions 52 are formed pixel by pixel ina P-type (a first conductivity type) semiconductor region 51, forexample, so that photodiodes PD are formed on a pixel-by-pixel basis.The P-type semiconductor region 51 provided on both the front and backsurfaces of the semiconductor substrate 41 also serves as a hole chargestorage region for reducing dark current.

The upper surface of the semiconductor substrate 41, which is the upperside in FIG. 2, is the back surface of the semiconductor substrate 41,and is a light incident surface through which light enters. Anantireflective film 43 is formed on the upper surface on the backsurface side of the semiconductor substrate 41.

The antireflective film 43 has a stack structure in which a fixed chargefilm and an oxide film are stacked, for example, and ahigh-dielectric-constant (high-k) insulating thin film formed by atomiclayer deposition (ALD), for example, may be used as the antireflectivefilm 43. Specifically, hafnium oxide (HfO₂), aluminum oxide (Al₂O₃),titanium oxide (TiO₂), strontium titan oxide (STO), or the like may beused. In the example illustrated in FIG. 2, the antireflective film 43is formed with a hafnium oxide film 53, an aluminum oxide film 54, and asilicon oxide film 55 that are stacked. Interpixel light blocking films45 that prevent incident light from entering adjacent pixels are formedon the upper surface of the antireflective film 43 and at the boundaryportions 44 (hereinafter also referred to as the pixel boundary portions44) between the pixels 10 adjacent to one another in the semiconductorsubstrate 41. The material of the interpixel light blocking films 45 maybe any material that blocks light, and it is possible to use a metalmaterial such as tungsten (W), aluminum (Al), or copper (Cu), forexample.

On the upper surface of the antireflective film 43 and the uppersurfaces of the interpixel light blocking films 45, a planarization film46 is formed with an insulating film of silicon oxide (SiO₂), siliconnitride (SiN), silicon oxynitride (SiON), or the like, or an organicmaterial such as resin, for example.

Further, on-chip lenses 47 are formed on the upper surfaces of theplanarization film 46 for the respective pixels. For example, theon-chip lenses 47 are formed with a resin material such as styreneresin, acrylic resin, styrene-acrylic copolymer resin, or siloxaneresin. The light gathered by the on-chip lenses 47 is efficiently madeto enter the photodiode PD. Further, at the pixel boundary portions 44on the back surface side of the semiconductor substrate 41, interpixelseparation portions 61 that separate adjacent pixels from one anotherare formed in the depth direction of the semiconductor substrate 41, toreach a predetermined depth in the substrate depth direction from theback surface side of the semiconductor substrate 41 (on the side of theon-chip lenses 47). The outer peripheral portions including the bottomand side walls of the interpixel separation portions 61 are covered withthe hafnium oxide film 53, which is part of the antireflective film 43.The interpixel separation portions 61 prevent incident light fromreaching the adjacent pixels 10, and confine the incident light in therespective pixels. The interpixel separation portions 61 also preventleakage of incident light from the adjacent pixels 10.

In the example illustrated in FIG. 2, the silicon oxide film 55, whichis the material of the uppermost layer of the antireflective film 43, isburied in trenches (grooves) dug from the back surface side, so that thesilicon oxide film 55 and the interpixel separation portions 61 aresimultaneously formed. Accordingly, the silicon oxide film 55, which ispart of the stack film serving as the antireflective film 43, is formedwith the same material as the interpixel separation portions 61, but isnot necessarily formed with the same material. The material to be buriedas the interpixel separation portions 61 in the trenches (grooves) dugfrom the back surface side may be a metal material such as tungsten (W),aluminum (Al), titanium (Ti), or titanium nitride (TiN), for example.

Meanwhile, on the front surface side of the semiconductor substrate 41on which the multilayer wiring layer 42 is formed, two transfertransistors TRG1 and TRG2 are formed for the one photodiode PD formed ineach pixel 10. Further, on the front surface side of the semiconductorsubstrate 41, floating diffusion regions FD1 and FD2 as charge storageportions that temporarily hold the charges transferred from thephotodiodes PD are formed with high-concentration N-type semiconductorregions (N-type diffusion regions).

The multilayer wiring layer 42 includes a plurality of metal films M andan interlayer insulating film 62 between the metal films M. FIG. 2 showsan example in which the metal films M include three layers: a firstmetal film M1 through a third metal film M3.

Of the plurality of metal films M in the multilayer wiring layer 42, aregion of the first metal film M1 closest to the semiconductor substrate41 and located below the formation region of each photodiode PD, or theregion overlapping at least part of the formation region of eachphotodiode PD in plan view, has a metal wiring line of copper, aluminum,or the like formed as a light blocking member 63.

The light blocking member 63 blocks infrared light that has entered thesemiconductor substrate 41 from the light incident surface via theon-chip lens 47, and passed through the semiconductor substrate 41without being photoelectrically converted in the semiconductor substrate41, with the first metal film M1 closest to the semiconductor substrate41, so that the infrared light does not reach the second metal film M2and the third metal film M3 located below the first metal film M1. Byvirtue of this light blocking function, the infrared light that has notbeen photoelectrically converted in the semiconductor substrate 41 andhas passed through the semiconductor substrate 41 is prevented frombeing scattered by the metal films M below the first metal film M1 andentering the neighboring pixels. Thus, it is possible to preventerroneous light detection at the neighboring pixels.

Further, the light blocking members 63 also has a function to reflectinfrared light that has entered the semiconductor substrate 41 from thelight incident surface via the on-chip lenses 47 and passed through thesemiconductor substrate 41 without being photoelectrically converted inthe semiconductor substrate 41, so that the infrared light reenters thesemiconductor substrate 41. In view of this, the light blocking members63 may also be regarded as reflective members. With this reflectivefunction, the amount of infrared light to be photoelectrically convertedin the semiconductor substrate 41 can be increased, and the quantumefficiency (QE), which is the sensitivity of the pixels 10 to infraredlight, can be improved.

Note that the light blocking members 63 may also form a structure thatreflects or blocks light with polysilicon, an oxide film, or the like,other than a metal material. Further, each light blocking member 63 maynot be formed with a single metal film M, but may be formed with aplurality of metal films M, such as a grid-like structure formed withthe first metal film M1 and the second metal film M2, for example.

Of the plurality of metal films M in the multilayer wiring layer 42, apredetermined metal film M, such as the second metal film M2, has wiringcapacitors 64 that are patterns formed in a comb-like shape, forexample. The light blocking members 63 and the wiring capacitors 64 maybe formed in the same layer (metal film M). In a case where the lightblocking members 63 and the wiring capacitors 64 are formed in differentlayers, however, the wiring capacitors 64 formed in a layer farther fromthe semiconductor substrate 41 than the light blocking members 63. Inother words, the light blocking members 63 are formed closer to thesemiconductor substrate 41 than the wiring capacitors 64.

As described above, the light receiving element 1 has a back-illuminatedstructure in which the semiconductor substrate 41 that is asemiconductor layer is disposed between the on-chip lenses 47 and themultilayer wiring layer 42, and incident light is made to enter thephotodiodes PD from the back surface side on which the on-chip lenses 47are formed.

Further, the pixels 10 each include two transfer transistors TRG1 andTRG2 for the photodiode PD provided in each pixel, and are designed tobe capable of distributing charges (electrons) generated throughphotoelectric conversion performed by the photodiode PD to the floatingdiffusion region FD1 or FD2.

Furthermore, the pixels 10 in the first example configuration have theinterpixel separation portions 61 formed at the pixel boundary portions44, to prevent incident light from reaching the adjacent pixels 10, andprevent leakage of incident light from the adjacent pixels 10 whileconfining the incident light in the respective pixels. The lightblocking members 63 are then formed in a metal film M below theformation regions of the photodiodes PD, so that infrared light that haspassed through the semiconductor substrate 41 without beingphotoelectrically converted in the semiconductor substrate 41 isreflected by the light blocking members 63 and is made to reenter thesemiconductor substrate 41. With the above configuration, the amount ofinfrared light to be photoelectrically converted in the semiconductorsubstrate 41 can be increased, and the quantum efficiency (QE), which isthe sensitivity of the pixels 10 to infrared light, can be improved.

<3. Example Circuit Configuration of a Pixel>

FIG. 3 shows the circuit configuration of each of the pixels 10two-dimensionally arranged in the pixel array unit 21.

A pixel 10 includes a photodiode PD as a photoelectric conversionelement. The pixel 10 also includes two sets of a transfer transistorTRG, a floating diffusion region FD, an additional capacitor FDL, aswitch transistor FDG, an amplification transistor AMP, a resettransistor RST, and a selection transistor SEL. The pixel 10 furtherincludes a charge ejection transistor OFG.

Here, in a case where the two sets of a transfer transistor TRG, afloating diffusion region FD, an additional capacitor FDL, a switchtransistor FDG, an amplification transistor AMP, a reset transistor RST,and a selection transistor SEL are distinguished from each other in thepixel 10, the transistors are referred to as transfer transistors TRG1and TRG2, floating diffusion regions FD1 and FD2, additional capacitorsFDL1 and FDL2, switch transistors FDG1 and FDL2, amplificationtransistors AMP1 and AMP2, reset transistors RST1 and RST2, andselection transistors SEL1 and SEL2, as shown in FIG. 3.

The transfer transistors TRG, the switch transistors FDG, theamplification transistors AMP, the selection transistors SEL, the resettransistors RST, and the charge ejection transistor OFG include N-typeMOS transistors, for example.

When a transfer drive signal TRG1 g supplied to the gate electrode ofthe transfer transistor TRG1 enters an active state, the transfertransistor TRG1 enters a conductive state, to transfer the chargesaccumulated in the photodiode PD to the floating diffusion region FD1.When a transfer drive signal TRG2 g supplied to the gate electrode ofthe transfer transistor TRG2 enters an active state, the transfertransistor TRG2 enters a conductive state, to transfer the chargesaccumulated in the photodiode PD to the floating diffusion region FD2.The floating diffusion regions FD1 and FD2 are charge storage portionsthat temporarily hold the charge transferred from the photodiode PD.

When an FD drive signal FDG1 g supplied to the gate electrode of theswitch transistor FDG1 enters an active state, the switch transistorFDG1 enters a conductive state, to connect the additional capacitor FDL1to the floating diffusion region FD1. When an FD drive signal FDG2 gsupplied to the gate electrode of the switch transistor FDG2 enters anactive state, the switch transistor FDG2 enters a conductive state, toconnect the additional capacitor FDL2 to the floating diffusion regionFD2. The additional capacitors FDL1 and FDL2 are formed with the wiringcapacitor 64 shown in FIG. 2.

When a reset drive signal RSTg supplied to the gate electrode of thereset transistor RST1 enters an active state, the reset transistor RST1enters a conductive state, to reset the potential of the floatingdiffusion region FD1. When a reset drive signal RSTg supplied to thegate electrode of the reset transistor RST2 enters an active state, thereset transistor RST2 enters a conductive state, to reset the potentialof the floating diffusion region FD2. Note that, when the resettransistors RST1 and RST2 are made to enter an active state, the switchtransistors FDG1 and FDG2 are also made to enter an active state at thesame time, and further, the additional capacitors FDL1 and FDL2 arereset.

For example, at a high-illuminance time at which the amount of incidentlight is large, the vertical drive unit 22 causes the switch transistorsFDG1 and FDG2 to enter an active state, to connect the floatingdiffusion region FD1 and the additional capacitor FDL1, and connect thefloating diffusion region FD2 and the additional capacitor FDL2. Thus,more charges can be accumulated at a high-illuminance time.

At a low-illuminance time at which the amount of incident light issmall, on the other hand, the vertical drive unit 22 causes the switchtransistors FDG1 and FDG2 to enter an inactive state, to disconnect theadditional capacitors FDL1 and FDL2 from the floating diffusion regionsFD1 and FD2, respectively. Thus, conversion efficiency can be increased.

When an ejection drive signal OFG1 g supplied to the gate electrode ofthe charge ejection transistor OFG enters an active state, the chargeejection transistor OFG enters a conductive state, to eject the chargesaccumulated in the photodiode PD.

When the source electrode of the amplification transistor AMP1 isconnected to a vertical signal line 29A via the selection transistorSEL1, the amplification transistor AMP1 is connected to a constantcurrent source (not shown), to form a source follower circuit. When thesource electrode of the amplification transistor AMP2 is connected to avertical signal line 29B via the selection transistor SEL2, theamplification transistor AMP2 is connected to a constant current source(not shown), to form a source follower circuit.

The selection transistor SEL1 is connected between the source electrodeof the amplification transistor AMP1 and the vertical signal line 29A.When a selection signal SEL1 g supplied to the gate electrode of theselection transistor SEL1 enters an active state, the selectiontransistor SEL1 enters a conductive state, to output a detection signalVSL1 output from the amplification transistor AMP1 to the verticalsignal line 29A.

The selection transistor SEL2 is connected between the source electrodeof the amplification transistor AMP2 and the vertical signal line 29B.When a selection signal SEL2 g supplied to the gate electrode of theselection transistor SEL2 enters an active state, the selectiontransistor SEL2 enters a conductive state, to output a detection signalVSL2 output from the amplification transistor AMP2 to the verticalsignal line 29B.

The transfer transistors TRG1 and TRG2, the switch transistors FDG1 andFDG2, the amplification transistors AMP1 and AMP2, the selectiontransistors SEL1 and SEL2, and the charge ejection transistor OFG of thepixel 10 are controlled by the vertical drive unit 22.

In the pixel circuit shown in FIG. 2, the additional capacitors FDL1 andFDL2, and the switch transistors FDG1 and FDG2 that control connectionof the additional capacitors FDL1 and FDL2 may be omitted. However, asthe additional capacitors FDL are provided and are appropriately useddepending on the amount of incident light, a high dynamic range can besecured.

Operation of the pixel 10 is now briefly described. First, before lightreception is started, a reset operation for resetting the charges in thepixel 10 is performed in all the pixels. Specifically, the chargeejection transistor OFG, the reset transistors RST1 and RST2, and theswitch transistors FDG1 and FDG2 are turned on, and the stored chargesin the photodiode PD, the floating diffusion regions FD1 and FD2, andthe additional capacitors FDL1 and FDL2 are ejected.

After the stored charges are ejected, light reception is started in allthe pixels.

During the light reception period, the transfer transistors TRG1 andTRG2 are alternately driven.

Specifically, during a first period, control is performed, to turn onthe transfer transistor TRG1, and turn off the transfer transistor TRG2.During the first period, the charges generated in the photodiode PD aretransferred to the floating diffusion region FD1. During a second periodfollowing the first period, control is performed, to turn off thetransfer transistor TRG1, and turn on the transfer transistor TRG2.During the second period, the charges generated in the photodiode PD aretransferred to the floating diffusion region FD2. As a result, thecharges generated in the photodiode PD are distributed to the floatingdiffusion regions FD1 and FD2, and are accumulated therein.

Here, the transfer transistor TRG and the floating diffusion region FDfrom which charges (electrons) obtained through photoelectric conversionare read out are also referred to as the active tap. Conversely, thetransfer transistor TRG and the floating diffusion region FD from whichno charges obtained through photoelectric conversion are read out arealso referred to as the inactive tap.

When the light reception period comes to an end, the respective pixels10 in the pixel array unit 21 are then selected in the order of thelines. In the selected pixel 10, the selection transistors SEL1 and SEL2are turned on. As a result, the charges accumulated in the floatingdiffusion region FD1 are output as the detection signal VSL1 to thecolumn processing unit 23 via the vertical signal line 29A. The chargesaccumulated in the floating diffusion region FD2 are output as thedetection signal VSL2 to the column processing unit 23 via the verticalsignal line 29B.

One light receiving operation is completed in the above manner, and thenext light receiving operation starting from a reset operation is thenperformed.

The reflected light to be received by the pixel 10 is delayed from thetime when the light source emitted light, in accordance with thedistance to the object.

Since the distribution ratio between the charges accumulated in the twofloating diffusion regions FD1 and FD2 varies depending on the delaytime corresponding to the distance to the object, the distance to theobject can be calculated from the distribution ratio between the chargesaccumulated in the two floating diffusion regions FD1 and FD2.

<4. Plan View of a Pixel>

FIG. 4 is a plan view showing an example of arrangement in the pixelcircuit shown in FIG. 3.

The lateral direction in FIG. 4 corresponds to the row direction(horizontal direction) in FIG. 1, and the longitudinal directioncorresponds to the column direction (vertical direction) in FIG. 1.

As shown in FIG. 4, the photodiode PD is formed with an N-typesemiconductor region 52 in the central region of the rectangular pixel10.

Outside the photodiode PD, the transfer transistor TRG1, the switchtransistor FDG1, the reset transistor RST1, the amplification transistorAMP1, and the selection transistor SEL1 are linearly arranged along apredetermined side of the four sides of the rectangular pixel 10, andthe transfer transistor TRG2, the switch transistor FDG2, the resettransistor RST2, the amplification transistor AMP2, and the selectiontransistor SEL2 are linearly arranged along another side of the foursides of the rectangular pixel 10.

Further, the charge ejection transistor OFG is disposed along a sidedifferent from the two sides of the pixel 10 along which the transfertransistors TRG, the switch transistors FDG, the reset transistors RST,the amplification transistors AMP, and the selection transistors SEL areformed.

Note that the arrangement in the pixel circuit shown in FIG. 3 is notlimited to this example, and may be some other arrangement.

<5. Another Example Circuit Configuration of a Pixel>

FIG. 5 shows another example circuit configuration of each pixel 10.

In FIG. 5, the components equivalent to those shown in FIG. 3 aredenoted by the same reference numerals as those used in FIG. 3, andexplanation of the components will not be repeated below.

A pixel 10 includes a photodiode PD as a photoelectric conversionelement. The pixel 10 also includes two sets of a first transfertransistor TRGa, a second transfer transistor TRGb, a memory MEM, afloating diffusion region FD, a reset transistor RST, an amplificationtransistor AMP, and a selection transistor SEL.

Here, in a case where the two sets of a first transfer transistor TRGa,a second transfer transistor TRGb, a memory MEM, a floating diffusionregion FD, a reset transistor RST, an amplification transistor AMP, anda selection transistor SEL are distinguished from each other in thepixel 10, the transistors are referred to as first transfer transistorsTRGa1 and TRGa2, second transfer transistors TRGb1 and TRGb2, transfertransistors TRG1 and TRG2, memories MEM1 and MEM2, floating diffusionregions FD1 and FD2, amplification transistors AMP1 and AMP2, andselection transistors SEL1 and SEL2, as shown in FIG. 5.

Accordingly, the pixel circuit in FIG. 5 differs from the pixel circuitin FIG. 3 in that the transfer transistors TRG are replaced with the twokinds transfer transistors, which are the first transfer transistorsTRGa and the second transfer transistors TRGb, and the memories MEM areadded. Further, the additional capacitors FDL and the switch transistorsFDG are omitted.

The first transfer transistors TRGa, the second transfer transistorsTRGb, the reset transistors RST, the amplification transistors AMP, andthe selection transistors SEL include N-type MOS transistors, forexample.

In the pixel circuit shown in FIG. 3, charges generated in thephotodiode PD are transferred to and held in the floating diffusionregions FD1 and FD2. In the pixel circuit in FIG. 5, on the other hand,charges generated in the photodiode PD are transferred to and held inthe memories MEM1 and MEM2 provided as charge storage portions.

Specifically, when a first transfer drive signal TRGa1 g supplied to thegate electrode of the first transfer transistor TRGa1 enters an activestate, the first transfer transistor TRGa1 enters a conductive state, totransfer the charges accumulated in the photodiode PD to the memoryMEM1. When a first transfer drive signal TRGa2 g supplied to the gateelectrode of the first transfer transistor TRGa2 enters an active state,the first transfer transistor TRGa2 enters a conductive state, totransfer the charges accumulated in the photodiode PD to the memoryMEM2.

Further, when a second transfer drive signal TRGb1 g supplied to thegate electrode of the second transfer transistor TRGb1 enters an activestate, the second transfer transistor TRGb1 enters a conductive state,to transfer the charges accumulated in the memory MEM1 to the floatingdiffusion region FD1. When a second transfer drive signal TRGb2 gsupplied to the gate electrode of the second transfer transistor TRGb2enters an active state, the second transfer transistor TRGb2 enters aconductive state, to transfer the charges accumulated in the memory MEM2to the floating diffusion region FD2.

When a reset drive signal RST1 g supplied to the gate electrode of thereset transistor RST1 enters an active state, the reset transistor RST1enters a conductive state, to reset the potential of the floatingdiffusion region FD1. When a reset drive signal RST2 g supplied to thegate electrode of the reset transistor RST2 enters an active state, thereset transistor RST2 enters a conductive state, to reset the potentialof the floating diffusion region FD2. Note that, when the resettransistors RST1 and RST2 are made to enter an active state, the secondtransfer transistors TRGb1 and TRGb2 are also made to enter an activestate at the same time, and further, the memories MEM1 and MEM2 arereset.

In the pixel circuit in FIG. 5, the charges generated in the photodiodePD are distributed to the memories MEM1 and MEM2, and are accumulatedtherein. At the timing of readout, the charges stored in the memoriesMEM1 and MEM2 are then transferred to the floating diffusion regions FD1and FD2, respectively, and are output from the pixel 10. <6. Plan Viewof a Pixel>

FIG. 6 is a plan view showing an example of arrangement in the pixelcircuit shown in FIG. 5.

The lateral direction in FIG. 6 corresponds to the row direction(horizontal direction) in FIG. 1, and the longitudinal directioncorresponds to the column direction (vertical direction) in FIG. 1.

As shown in FIG. 6, the photodiode PD is formed with an N-typesemiconductor region 52 in the central region of the rectangular pixel10.

Outside the photodiode PD, the first transfer transistor TRGa1, thesecond transfer transistor TRGb1, the reset transistor RST1, theamplification transistor AMP1, and the selection transistor SEL1 arelinearly arranged along a predetermined side of the four sides of therectangular pixel 10, and the first transfer transistor TRGa2, thesecond transfer transistor TRGb2, the reset transistor RST2, theamplification transistor AMP2, and the selection transistor SEL2 arelinearly arranged along another side of the four sides of therectangular pixel 10. The memories MEM1 and MEM2 are formed with buriedN-type diffusion regions, for example.

Note that the arrangement in the pixel circuit shown in FIG. 5 is notlimited to this example, and may be some other arrangement.

<7. Effects of a Back-Illuminated Type>

With the light receiving element 1 described above, the followingeffects can be achieved.

First, since the light receiving element 1 is of a back-illuminatedtype, quantum efficiency (QE)×aperture ratio (fill factor (FF)) can bemaximized, and the ranging characteristics of the light receivingelement 1 can be improved.

For example, as indicated by an arrow W11 in FIG. 7, a normalsurface-illuminated image sensor has a structure in which wiring lines102 and wiring lines 103 are formed on the light incident surface sidethrough which light from outside enters a PD 101 that is a photoelectricconversion portion.

Therefore, part of light that obliquely enters the PD 101 from outsideat a certain angle as shown by an arrow A21 and an arrow A22, forexample, might be blocked by the wiring lines 102 or the wiring lines103, and does not enter the PD 101.

On the other hand, a back-illuminated image sensor has a structure inwhich wiring lines 105 and wiring lines 106 are formed on the surface onthe opposite side from the light incident surface through which lightfrom outside enters a PD 104 that is a photoelectric conversion portion,as indicated by an arrow W12, for example. Accordingly, it is possibleto secure a sufficient aperture ratio, compared with that in a case witha surface-illuminated type. Specifically, as indicated by an arrow A23and an arrow A24, for example, light obliquely incident on the PD 104 ata certain angle enters the PD 104 from outside without being blocked byany wiring line. Thus, a larger amount of light can be received, andpixel sensitivity can be improved.

The pixel sensitivity improving effect achieved with such aback-illuminated type can also be achieved with the light receivingelement 1, which is a back-illuminated ToF sensor.

Specifically, in the structure of a surface-illuminated ToF sensor,wiring lines 112 and wiring lines 113 are formed on the light incidentsurface side of a PD 111 that is a photoelectric conversion portion, asindicated by an arrow W13. Therefore, part of light that obliquelyenters the PD 111 from outside at a certain angle as shown by an arrowA25 and an arrow A26, for example, might be blocked by the wiring lines112 or the wiring lines 113 or the like, and does not enter the PD 111.On the other hand, a back-illuminated ToF sensor has a structure inwhich transfer transistors for reading out charges are formed on thesurface on the opposite side from the light incident surface of a PD 115that is a photoelectric conversion portion, as indicated by an arrowW14, for example. Further, wiring lines 117 and wiring lines 118 areformed on the surface on the opposite side from the light incidentsurface of the PD 115. With this arrangement, as indicated by an arrowA28 and an arrow A29, for example, light obliquely incident on the PD115 at a certain angle enters the PD 115 without being blocked by anywiring line.

Accordingly, in the back-illuminated ToF sensor, a sufficient apertureratio can be secured compared with that in a case with asurface-illuminated ToF sensor. Thus, quantum efficiency (QE)×apertureratio (FF) can be maximized, and the ranging characteristics can beimproved.

FIG. 8 shows cross-sectional views of pixels of a surface-illuminatedToF sensor and a back-illuminated ToF sensor.

In the surface-illuminated ToF sensor on the left side in FIG. 8, theupper side of a substrate 141 in the drawing is the light incidentsurface, and a wiring layer 152 including a plurality of wiring lines,an interpixel light blocking film 153, and an on-chip lens 154 arestacked on the light incident surface side of the substrate 141.

In the back-illuminated ToF sensor on the right side in FIG. 8, a wiringlayer 152 including a plurality of wiring lines is formed on the lowerside of a substrate 142 on the opposite side from the light incidentsurface in the drawing, and an interpixel light blocking film 153 and anon-chip lens 154 are stacked on the upper side of the substrate 142,which is the light incident surface side.

Note that, in FIG. 8, each shaded trapezoidal shape indicates a regionin which the light intensity is high because infrared light is gatheredby the on-chip lens 154.

For example, in the surface-illuminated ToF sensor, there is a regionR11 in which charge readout transfer transistors TG1 and TG2 exist onthe light incident surface side of the substrate 141. In thesurface-illuminated ToF sensor, the intensity of infrared light is highin the region R11 near the light incident surface of the substrate 141,and accordingly, the probability of photoelectric conversion of infraredlight in the region R11 is high. That is, since the amount of infraredlight entering the area near the inactive tap is large, the number ofsignal carriers that are not detected by the active tap increases, andcharge separation efficiency decreases.

In the back-illuminated ToF sensor, on the other hand, there is a regionR12 in which the active tap and the inactive tap are formed at positionsfar from the light incident surface of the substrate 142, or atpositions near the surface on the opposite side from the light incidentsurface side. The substrate 142 corresponds to the semiconductorsubstrate 41 shown in FIG. 2.

The region R12 is located at a portion of the surface on the oppositeside from the light incident surface side of the substrate 142, and theregion R12 is also located at a position far from the light incidentsurface.

Accordingly, in the vicinity of the region R12, the intensity ofincident infrared light is relatively low. Signal carriers obtainedthrough photoelectric conversion in a region in which the intensity ofinfrared light is high, such as a region near the center of thesubstrate 142 or near the light incident surface, are guided to theactive tap by the electric field gradient formed by the active tap andthe inactive tap, and are detected in the floating diffusion region FDof the active tap. In the vicinity of the region R12 including theinactive tap, on the other hand, the intensity of incident infraredlight is relatively low, and accordingly, the probability ofphotoelectric conversion of infrared light in the region R12 is low.That is, the amount of infrared light entering an area in the vicinityof the inactive tap is small. Accordingly, the number of signal carriers(electrons) that are generated through photoelectric conversion in thevicinity of the inactive tap and move to the floating diffusion regionFD of the inactive tap becomes smaller, and thus, the charge separationefficiency can be improved. As a result, the ranging characteristics canbe improved.

Further, in the back-illuminated light receiving element 1, thethickness of the semiconductor substrate 41 can be reduced, and thus, itis possible to increase the efficiency in extracting electrons (charges)that are signal carriers.

For example, in a surface-illuminated ToF sensor, it is difficult tosecure a sufficient aperture ratio. Therefore, to secure a higherquantum efficiency and prevent a decrease in quantum efficiency×apertureratio, there is a need to increase the thickness of a substrate 171 to acertain value, as indicated by an arrow W31 in FIG. 9.

As a result, the potential gradient becomes lower in the region near thesurface on the opposite side from the light incident surface in thesubstrate 171, or in a region R21, for example, and the electric fieldin a direction perpendicular to the substrate 171 substantially becomesweaker. In this case, the moving velocity of the signal carriers becomeslower, and therefore, the time elapsing from the photoelectricconversion to the transfer of the signal carriers to the floatingdiffusion region FD of the active tap becomes longer. Note that, in FIG.9, the arrows in the substrate 171 indicate the electric field in thedirection perpendicular to the substrate 171 in the substrate 171.

Further, when the substrate 171 is thick, the moving distance of thesignal carriers from a position far from the active tap in the substrate171 to the floating diffusion region FD of the active tap is long.

Accordingly, at the position far from the active tap, the time elapsingfrom the photoelectric conversion to the transfer of the signal carriersto the floating diffusion region FD of the active tap becomes evenlonger.

Therefore, after switching of the transfer transistors TG is completed,some signal carriers might reach the active tap, and turn into anerroneous signal.

FIG. 10 shows the relationship between the position in the thicknessdirection of the substrate 171 and the moving velocity of the signalcarriers. The region R21 corresponds to a diffusion current region.

In a case where the substrate 171 is thick as described above, when thedrive frequency is high, or when switching between the active tap andthe inactive tap is performed at high speed, for example, electronsgenerated at a position far from the active tap, such as the region R21,are not completely drawn into the floating diffusion region FD of theactive tap. In other words, in a case where the time during which thetap is active is short, some electrons (charges) generated in the regionR21 or the like are not detected in the floating diffusion region FD ofthe active tap, and the electron extraction efficiency becomes lower.

In the back-illuminated ToF sensor, on the other hand, a sufficientaperture ratio can be secured. Thus, even when a substrate 172 is madethinner as indicated by an arrow W32 in FIG. 9, for example, sufficientquantum efficiency×aperture ratio can be secured. Here, the substrate172 corresponds to the semiconductor substrate 41 in FIG. 2, and thearrows in the substrate 172 indicate the electric field in a directionperpendicular to the substrate 172.

FIG. 11 shows the relationship between the position in the thicknessdirection of the substrate 172 and the moving velocity of the signalcarriers.

When the thickness of the substrate 172 is reduced in this manner, theelectric field in a direction perpendicular to the substrate 172 becomessubstantially stronger, and only the electrons (charges) in a driftcurrent region in which the moving velocity of the signal carriers ishigh are used while the electrons in the diffusion current region inwhich the moving velocity of the signal carriers is low are not used. Asonly the electrons (charges) in the drift current region are used, thetime elapsing from the photoelectric conversion to detection of thesignal carriers in the floating diffusion region FD of the active tapbecomes shorter.

Further, as the thickness of the substrate 172 becomes smaller, themoving distance of the signal carriers to the floating diffusion regionFD of the active tap also becomes shorter.

In view of the above facts, in the back-illuminated ToF sensor, evenwhen the drive frequency is high, the signal carriers (electrons)generated in the respective regions in the substrate 172 can besufficiently drawn into the floating diffusion region FD of the activetap, and thus, the electron extraction efficiency can be increased.

Further, as the thickness of the substrate 172 is reduced, sufficientelectron extraction efficiency can be secured even at a high drivefrequency, and resistance to high-speed drive can be increased.

Particularly, in the back-illuminated ToF sensor, a sufficient apertureratio can be obtained. Thus, the pixels can be miniaturized accordingly,and the miniaturization resistance of the pixels can be increased.

Furthermore, as the light receiving element 1 is of a back-illuminatedtype, freedom is allowed in the back end of line (BEOL) design, andthus, it is possible to increase the degree of freedom in setting asaturation signal amount (Qs).

<8. Cross-Sectional View of a Second Example Configuration of Pixels>

FIG. 12 is a cross-sectional view showing a second example configurationof the pixels 10.

In FIG. 12, the components equivalent to those of the first exampleconfiguration shown in FIG. 2 are denoted by the same reference numeralsas those used in FIG. 2, and explanation of the components will not beunnecessarily repeated.

The second example configuration in FIG. 12 is the same as the firstexample configuration in FIG. 2, except that the interpixel separationportions 61 that are deep trench isolation (DTI) formed by digging fromthe back surface side (the side of the on-chip lenses 47) of thesemiconductor substrate 41 are replaced with interpixel separationportions 211 penetrating the semiconductor substrate 41.

The interpixel separation portions 211 are formed in the followingmanner: trenches are formed from the back surface side (the side of theon-chip lenses 47) or from the front surface side of the semiconductorsubstrate 41 until reaching the substrate surface on the opposite side,and the trenches are filled with the silicon oxide film 55, which is thematerial of the uppermost layer of the antireflective film 43. Thematerial to be buried as the interpixel separation portions 211 in thetrenches may be a metal material such as tungsten (W), aluminum (Al),titanium (Ti), or titanium nitride (TiN), for example, other than aninsulating film such as the silicon oxide film 55.

As such interpixel separation portions 211 are formed, it is possible tocompletely separate adjacent pixels electrically from each other. As aresult, the interpixel separation portions 211 prevent incident lightfrom reaching the neighboring pixels 10, and confine the incident lightin the respective pixels. The interpixel separation portions 211 alsoprevent leakage of incident light from the adjacent pixels 10.

As the second example configuration is also a pixel structure of aback-illuminated type, a sufficient aperture ratio can be securedcompared with that in a case with a surface-illuminated structure. Thus,quantum efficiency (QE)×aperture ratio (FF) can be maximized.

Further, of the plurality of metal films M in the multilayer wiringlayer 42, the first metal film M1 closest to the semiconductor substrate41 has the light blocking members (the reflective members) 63 in regionslocated below the formation regions of the photodiodes PD, so thatinfrared light that has not been photoelectrically converted in thesemiconductor substrate 41 and has passed through the semiconductorsubstrate 41 is reflected by the light blocking members 63 and is madeto reenter the semiconductor substrate 41.

With this arrangement, the amount of infrared light to bephotoelectrically converted in the semiconductor substrate 41 can befurther increased, and the quantum efficiency (QE), which is thesensitivity of the pixels 10 to infrared light, can be improved.Further, the infrared light that has not been photoelectricallyconverted in the semiconductor substrate 41 and has passed through thesemiconductor substrate 41 is prevented from being scattered by themetal films M and entering the neighboring pixels. Thus, it is possibleto prevent erroneous light detection at the neighboring pixels.

<9. Cross-Sectional View of a Third Example Configuration of Pixels>

FIG. 13 is a cross-sectional view showing a third example configurationof the pixels 10.

In FIG. 13, the components equivalent to those of the first exampleconfiguration shown in FIG. 2 are denoted by the same reference numeralsas those used in FIG. 2, and explanation of the components will not beunnecessarily repeated.

In the third example configuration in FIG. 13, PD upper regions 223located above the formation regions of the photodiodes PD in (the P-typesemiconductor region 51 of) the semiconductor substrate 41 each have amoth-eye structure in which minute concavities and convexities areformed. Further, in conformity with the moth-eye structures in the PDupper regions 223 in the semiconductor substrate 41, an antireflectivefilm 221 formed on the upper surfaces thereof also has a moth-eyestructure. The antireflective film 221 is formed with a stack of ahafnium oxide film 53, an aluminum oxide film 54, and a silicon oxidefilm 55, as in the first example configuration.

As the PD upper regions 223 of the semiconductor substrate 41 aremoth-eye structures as described above, it is possible to alleviate theabrupt change in the refractive index at the substrate interface, andreduce the influence of reflected light.

Note that, in FIG. 13, the interpixel separation portions 61 formed withDTI formed by digging from the back surface side (the side of theon-chip lenses 47) of the semiconductor substrate 41 are formed to reachslightly deeper positions than the interpixel separation portions 61 ofthe first example configuration in FIG. 2. The depth in the substratethickness direction in which the interpixel separation portions 61 areformed may be set at any depth as above.

In the other aspects, the third example configuration is similar to thefirst example configuration.

<10. Cross-Sectional View of a Fourth Example Configuration of Pixels>

FIG. 14 is a cross-sectional view showing a fourth example configurationof the pixels 10.

In FIG. 14, the components equivalent to those of the first throughthird example configurations described above are denoted by the samereference numerals as those used above, and explanation of thecomponents will not be unnecessarily repeated.

The fourth example configuration in FIG. 14 is the same as the thirdexample configuration shown in FIG. 13 in that the PD upper regions 223each include a substrate interface having a moth-eye structure and theantireflective film 221.

The fourth example configuration in FIG. 14 is also the same as thesecond example configuration shown in FIG. 12 in including theinterpixel separation portions 211 penetrating the entire semiconductorsubstrate 41.

In other words, the fourth example configuration in FIG. 14 includesboth the interpixel separation portions 211 of the second exampleconfiguration, and the semiconductor substrate 41 and the antireflectivefilm 221 having moth-eye structures of the third example configuration.In the other aspects, the fourth example configuration is similar to thesecond example configuration or the third example configuration.

As the third and fourth example configurations are also pixel structuresof a back-illuminated type, a sufficient aperture ratio can be securedcompared with that in a case with a surface-illuminated structure. Thus,quantum efficiency (QE)×aperture ratio (FF) can be maximized.

Further, the light blocking member (the reflective member) 63 isprovided in a predetermined metal film M in the multilayer wiring layer42, the sensitivity of the pixels 10 to infrared light can be increased,and erroneous light detection at neighboring pixels can be prevented.

<11. Cross-Sectional View of a Fifth Example Configuration of Pixels>

FIG. 15 is a cross-sectional view showing a fifth example configurationof the pixels 10.

In FIG. 15, the components equivalent to those of the first throughfourth example configurations described above are denoted by the samereference numerals as those used above, and explanation of thecomponents will not be unnecessarily repeated.

In the first through fourth example configurations described above, theinterpixel separation portions 61 or the interpixel separation portions211 provided in the pixel boundary portions 44 may be omitted.

For example, if the interpixel separation portions 61 of the thirdexample configuration described above or the interpixel separationportions 211 of the fourth example configuration described above areomitted, the structure shown in FIG. 15 is obtained.

The fifth example configuration in FIG. 15 has the configuration of thethird example configuration minus the interpixel separation portions 61or the configuration of the fourth example configuration minus theinterpixel separation portions 211. In the fifth example configuration,the antireflective film 221 is formed as a flat film in each of thepixel boundary portions 44. In the other aspects, the fifth exampleconfiguration is similar to the third example configuration or thefourth example configuration.

<Perspective Views of Moth-Eye Structures>

FIG. 16A is a perspective view of a moth-eye structure formed in a PDupper region 223 of the semiconductor substrate 41.

In the moth-eye structure in the semiconductor substrate 41, a pluralityof quadrangular pyramidal regions of substantially the same shape havingits apex on the side of the semiconductor substrate 41 and ofsubstantially the same size is regularly arranged (in a grid-likepattern), as shown in FIG. 16A, for example.

Note that, in FIG. 16A, the upper side of the semiconductor substrate 41is the light incident side, which is the side of the on-chip lens 47.

The moth-eye structure is formed on the light incident surface side ofthe semiconductor substrate 41, and has an inverse pyramid structure inwhich a plurality of quadrangular pyramidal regions having their apexeson the side of the photodiode PD is regularly arranged. The bottomsurface of each quadrangular pyramid has a square shape, and thesemiconductor substrate 41 is dug so that each quadrangular pyramidalregion is convex on the side of the photodiode PD. In FIG. 16A, aportion indicated by an arrow W51 is the concave portion of the apexportion of each quadrangular pyramidal region on the side of thephotodiode PD, for example. The concave portion indicated by the arrowW51 has a curvature, and has a roundish shape, for example.

Note that not only the respective concave portions of the respectivequadrangular pyramids in the moth-eye structure but also the obliqueportions of the respective quadrangular pyramidal regions, which areshaded portions in FIG. 16B, may also have a certain curvature. As theoblique portions also have a curvature, it is possible to furtherimprove the effect to reduce formation unevenness and peeling of theplanarization film 46.

FIGS. 17A and 17B are perspective views showing another example of amoth-eye structure in the semiconductor substrate 41.

In the example described above with reference to FIGS. 16A and 16B, themoth-eye structure is an inverse pyramid structure formed withquadrangular pyramidal regions having apexes on the side of thephotodiode PD. However, the moth-eye structure may be a forward pyramidstructure as shown in FIGS. 17A and 17B, for example.

Specifically, as shown in FIG. 17A, the moth-eye structure is formed onthe surface of the semiconductor substrate 41 on the light incidentside. Further, the moth-eye structure is a forward pyramid structure inwhich a plurality of quadrangular pyramidal regions having apexes on theside of the on-chip lens 47, which is the light incident side, isregularly arranged in a grid-like pattern.

In FIG. 17A, the plurality of quadrangular pyramidal regions also hassubstantially the same shape and substantially the same size, and thebottom surface of each quadrangular pyramid has a square shape.

Furthermore, the semiconductor substrate 41 is dug to form thequadrangular pyramidal regions, so that the respective quadrangularpyramidal regions are convex on the opposite side from the side of thephotodiode PD.

For example, a portion indicated by an arrow W71 is the concave portionof the base portion of each quadrangular pyramidal region on the side ofthe photodiode PD. The concave portion indicated by the arrow W71 has aportion that is convex on the side of the photodiode PD when viewed in across-section substantially parallel to the direction from the lightincident side of the semiconductor substrate 41 toward the photodiodePD. The convex portion has a curvature, and has a roundish shape, as inthe example shown in FIGS. 16A and 16B.

In FIG. 17B, the shaded portions formed with the bases of the respectivequadrangular pyramids having apexes on the upper side may be formed tohave a curvature. In this case, it is possible to reduce formationunevenness and peeling of the planarization film 46 formed on thesemiconductor substrate 41, as in the example shown in FIGS. 16A and16B.

FIGS. 18A and 18B are perspective views showing other examples of amoth-eye structure in the semiconductor substrate 41.

In the moth-eye structure, the bottom surfaces of the minute concavitiesand convexities may have a rectangular shape, as shown in FIG. 18A, forexample.

The moth-eye structure shown in FIG. 18A is formed on the light incidentsurface side of the semiconductor substrate 41, and has long linearconcave portions in the longitudinal direction (vertical direction) orthe lateral direction (horizontal direction) of the pixel 10.

More specifically, the moth-eye structure shown in FIG. 18A has asaw-tooth shape when viewed in a cross-section in the same direction asthe cross-sectional views in FIGS. 13 through 15, and has a shape inwhich a plurality of triangular prisms of substantially the same shapeand substantially the same size is arranged in one direction while onevertex of each triangle and one rectangular surface of each triangularprism face the photodiode PD.

In FIG. 18A, a portion indicated by an arrow W91 is a concave portion,for example, and a portion indicated by an arrow W92 is a convexportion, for example. The shaded portion of each concave portion has aroundish shape with a predetermined curvature. Accordingly, it is alsopossible to reduce formation unevenness and peeling of the planarizationfilm 46 formed on the semiconductor substrate 41 in this example.

Further, other than a structure in which quadrangular pyramidal shapesof substantially the same size are regularly arranged, the moth-eyestructure in the semiconductor substrate 41 may be a structure in whichquadrangular pyramidal shapes of different sizes from one another may beirregularly arranged as shown in FIG. 18B.

The example shown in FIG. 18B is a forward pyramid structure in whichquadrangular pyramidal regions having apexes on the side of the on-chiplens 47 are irregularly arranged. Furthermore, the sizes of theplurality of quadrangular pyramidal regions are not the same size. Inother words, the sizes and the arrangement of the quadrangular pyramidsare random.

For example, portions indicated by an arrow W93 and an arrow W94 areconcave portions, and the concave portions have a curvature and haveroundish shapes. With this arrangement, it is possible to reduceformation unevenness and peeling of the planarization film 46 formed onthe semiconductor substrate 41.

FIG. 18B shows a moth-eye structure having a forward pyramid structurein which a plurality of quadrangular pyramidal regions having apexes onthe side of the on-chip lens 47 is randomly arranged. However, theinverse pyramid structure shown in FIGS. 16A and 16B may of course be astructure in which the sizes and the arrangement of the plurality ofquadrangular pyramidal regions are random.

The moth-eye structure of the semiconductor substrate 41 formed in thePD upper regions 223 can be formed to have the shape shown in any ofFIGS. 16A through 18B, for example. With this, it is possible toalleviate the sudden change in the refractive index at the substrateinterface, and reduce the influence of reflected light. Note that, inthe third through fifth example configurations in which a moth-eyestructure is adopted, in a case where the antireflection effect of themoth-eye structure is sufficient, the antireflective film 221 thereonmay be omitted.

<12. Cross-Sectional View of a Sixth Example Configuration of Pixels>

FIG. 19 is a cross-sectional view showing a sixth example configurationof the pixels 10.

In FIG. 19, the components equivalent to those of the first throughfifth example configurations described above are denoted by the samereference numerals as those used above, and explanation of thecomponents will not be unnecessarily repeated.

In the first through fifth example configurations described above, thelight receiving element 1 is formed with a single semiconductorsubstrate, or only with the semiconductor substrate 41. In the sixthexample configuration in FIG. 19, however, the light receiving element 1is formed with two semiconductor substrates: the semiconductor substrate41 and a semiconductor substrate 301. In the description below, for easyunderstanding, the semiconductor substrate 41 and the semiconductorsubstrate 301 will be also referred to as the first substrate 41 and thesecond substrate 301, respectively.

The sixth example configuration in FIG. 19 is similar to the firstexample configuration in FIG. 2 in that the interpixel light blockingfilms 45, the planarization film 46, and the on-chip lenses 47 areformed on the light incident surface side of the first substrate 41.

The sixth example configuration is also similar to the first exampleconfiguration in FIG. 2 in that the interpixel separation portions 6lareformed in the pixel boundary portions 44 on the back surface side of thefirst substrate 41.

The sixth example configuration is also similar to the first exampleconfiguration in that the photodiodes PD as the photoelectric conversionportions are formed in the first substrate 41 for the respective pixels,and in that the two transfer transistors TRG1 and TRG2, and the floatingdiffusion regions FD1 and FD2 as the charge storage portions are formedon the front surface side of the first substrate 41.

On the other hand, a different aspect from the first exampleconfiguration in FIG. 2 is that an insulating layer 313 of a wiringlayer 311 on the front surface side of the first substrate 41 is bondedto an insulating layer 312 of the second substrate 301.

The wiring layer 311 of the first substrate 41 includes at least onemetal film M, and the light blocking members 63 are formed with themetal film M in regions located below the formation regions of thephotodiodes PD. Pixel transistors Tr1 and Tr2 are formed at theinterface on the opposite side from the side of the insulating layer312, which is the bonding surface side of the second substrate 301. Thepixel transistors Tr1 and Tr2 are amplification transistors AMP andselection transistors SEL, for example.

In other words, in the first through fifth example configurations onlyincluding the single semiconductor substrate 41 (the first substrate41), all of the pixel transistors including the transfer transistorsTRG, the switch transistors FDG, the amplification transistors AMP, andthe selection transistors SEL are formed in the semiconductor substrate41. In the light receiving element 1 of the sixth example configurationincluding a stack structure of two semiconductor substrates, on theother hand, the pixel transistors other than the transfer transistorsTRG, or the switch transistors FDG, the amplification transistors AMP,and the selection transistors SEL are formed in the second substrate301. A multilayer wiring layer 321 including at least two metal films Mis formed on the opposite side of the second substrate 301 from the sideof the first substrate 41. The multilayer wiring layer 321 includes afirst metal film M11, a second metal film M12, and an interlayerinsulating film 333.

The transfer drive signal TRG1 g for controlling the transfertransistors TRG1 is supplied from the first metal film M1l of the secondsubstrate 301 to the gate electrodes of the transfer transistors TRG1 ofthe first substrate 41 by through silicon vias (TSVs) 331-1 penetratingthe second substrate 301. The transfer drive signal TRG2 g forcontrolling the transfer transistors TRG2 is supplied from the firstmetal film M1l of the second substrate 301 to the gate electrodes of thetransfer transistors TRG2 of the first substrate 41 by TSVs 331-2penetrating the second substrate 301.

Likewise, the charges accumulated in the floating diffusion regions FD1are transferred from the side of the first substrate 41 to the firstmetal film M1l of the second substrate 301 by TSVs 332-1 penetrating thesecond substrate 301. The charges accumulated in the floating diffusionregions FD2 are transferred from the side of the first substrate 41 tothe first metal film M1l of the second substrate 301 by TSVs 332-2penetrating the second substrate 301.

The wiring capacitors 64 are formed in a region (not shown) of the firstmetal film M1l or the second metal film M12. The metal film M in whichthe wiring capacitors 64 are formed is designed to have a high wiringdensity for capacitor formation, and the metal film M connected to thegate electrodes of the transfer transistors TRG, the switch transistorsFDG, or the like is designed to have a low wiring density to reduceinduced current. The wiring layer (metal film M) to be connected to thegate electrodes may vary with each pixel transistor.

As described above, the pixels 10 of the sixth example configuration canbe formed by stacking two semiconductor substrates: the first substrate41 and the second substrate 301. The pixel transistors other than thetransfer transistors TRG are formed in the second substrate 301, whichis different from the first substrate 41 including the photoelectricconversion portions. Further, the vertical drive unit 22 that controlsdriving of the pixels 10, the pixel drive lines 28, the vertical signallines 29 that transmit detection signals, and the like are also formedin the second substrate 301. Thus, the pixels can be miniaturized, andthe degree of freedom in the back end of line (BEOL) design becomeshigher.

As the sixth example configuration is also a pixel structure of aback-illuminated type, a sufficient aperture ratio can be securedcompared with that in a case with a surface-illuminated structure. Thus,quantum efficiency (QE)×aperture ratio (FF) can be maximized. Further,the regions of the wiring layer 311 that is the closest to the firstsubstrate 41 and overlaps the formation regions of the photodiodes PDinclude the light blocking members (the reflective members) 63, so thatinfrared light that has not been photoelectrically converted in thesemiconductor substrate 41 and has passed through the semiconductorsubstrate 41 is reflected by the light blocking members 63 and is madeto reenter the semiconductor substrate 41. With this arrangement, theamount of infrared light to be photoelectrically converted in thesemiconductor substrate 41 can be further increased, and the quantumefficiency (QE), which is the sensitivity of the pixels 10 to infraredlight, can be improved. Further, the infrared light that has not beenphotoelectrically converted in the semiconductor substrate 41 and haspassed through the semiconductor substrate 41 can be prevented fromentering the side of the second substrate 301.

<Manufacturing Method in the Sixth Example Configuration>

Referring now to FIGS. 20A through 20F, a manufacturing method in thesixth example configuration is described. First, as shown in FIG. 20A,after the photodiodes PD as the photoelectric conversion portions andthe floating diffusion regions FD are formed pixel by pixel inpredetermined regions in the first substrate 41, the gate electrodes 351of the transfer transistors TRG are formed.

Next, as shown in FIG. 20B, after an insulating film 361 is formed onthe gate electrodes 351 of the transfer transistors TRG and the uppersurface of the first substrate 41, the light blocking members 63corresponding to the regions of the photodiodes PD are formed as apattern.

Next, as shown in FIG. 20C, an insulating film is further stacked on thelight blocking members 63 and the insulating film 361, to form theinsulating layer 313, and the wiring layer 311 that is the front surfaceside of the first substrate 41 is formed. Then, the insulating layer 312on the back surface side of the second substrate 301 in which the pixeltransistors Tr1 and Tr2 such as the amplification transistors AMP andthe selection transistors SEL are formed in advance is bonded to theinsulating layer 313 of the first substrate 41.

Next, as shown in FIG. 20D, after an insulating layer 362 is formed onthe upper surface of the second substrate 301, trenches 371-1 and 371-2for contact with the gate electrodes of the pixel transistors Tr1 andTr2 are formed. Further, trenches 372-1, 372-2, 373-1, and 373-2penetrating the second substrate 301 are formed at the portionsnecessary for electrically connecting the first substrate 41 and thesecond substrate 301, such as the gate electrodes of the transfertransistors TRG1 and TRG2, and the floating diffusion regions FD1 andFD2. Next, as shown in FIG. 20E, the trenches 371-1 and 371-2, and thetrenches 372-1, 372-2, 373-1, and 373-2 are filled with a metal materialsuch as tungsten (W). As a result, the TSVs 331-1, 331-2, 332-1, and332-2 are formed.

Next, as shown in FIG. 20F, the first metal film M11, the second metalfilm M12, and an insulating layer are formed on the insulating layer362, and thus, the multilayer wiring layer 321 is formed.

After FIG. 20F, the antireflective film 43, the on-chip lenses 47, andthe like are formed on the back surface side that is the light incidentsurface of the first substrate 41. Thus, the light receiving element 1in FIG. 19 is completed.

Note that the sixth example configuration shown in FIG. 19 is aconfiguration formed by modifying the first example configuration shownin FIG. 2 into a stack structure of two semiconductor substrates.However, it is of course possible to adopt a configuration formed bymodifying any of the second through fifth example configurations into astack structure of two semiconductor substrates.

<13. Example of a Four-Tap Pixel Configuration>

Each pixel 10 in the first through sixth example configurations is aso-called two-tap pixel structure that has two transfer transistors TRG1and TRG2 as the transfer gates for one photodiode PD, has two floatingdiffusion regions FD1 and FD2 as charge storage portions, anddistributes charges generated in the photodiode PD to the two floatingdiffusion regions FD1 and FD2.

On the other hand, a pixel 10 may be a so-called four-tap pixelstructure that has four transfer transistors TRG1 through TRG4 andfloating diffusion regions FD1 through FD4 for one photodiode PD, anddistributes charges generated in the photodiode PD to the four floatingdiffusion regions FD1 through FD4.

FIG. 21 is a plan view of a pixel 10 in a case of a four-tap pixelstructure.

The pixel 10 includes four sets of a first transfer transistor TRGa, asecond transfer transistor TRGb, a reset transistor RST, anamplification transistor AMP, and a selection transistor SEL.

Outside the photodiode PD, one set of a first transfer transistor TRGa,a second transfer transistor TRGb, a reset transistor RST, anamplification transistor AMP, and a selection transistor SEL is linearlyarranged along each one side of the four sides of the rectangular pixel10.

In FIG. 21, each set of a first transfer transistor TRGa, a secondtransfer transistor TRGb, a reset transistor RST, an amplificationtransistor AMP, and a selection transistor SEL, which are arranged alongone of the four sides of the rectangular pixel 10, are denoted with oneof the numbers 1 through 4, and thus, is distinguished from the othersets.

As described above, a pixel 10 may have a structure that distributescharges generated in the photodiode PD to two taps, or a structure thatdistributes the charges to four taps. A pixel 10 does not necessarilyhave a two-tap structure, and may have a structure with three or moretaps.

For example, in a case where a pixel 10 has a two-tap structure, drivingis performed to distribute generated charges to the two floatingdiffusion regions FD by shifting the phase (the light reception timing)by 180 degrees between the first tap and the second tap. In a case wherea pixel 10 has a four-tap structure, on the other hand, driving may beperformed to distribute generated charges to four floating diffusionregions FD by shifting the phase (the light reception timing) by 90degrees between each two taps among the first through fourth taps. Thedistance to the object can be then determined, on the basis of thedistribution ratio of the charges accumulated in the four floatingdiffusion regions FD.

<14. Example Configuration of a Ranging Module>

FIG. 22 is a block diagram showing an example configuration of a rangingmodule that outputs ranging information, using the light receivingelement 1 described above.

A ranging module 500 includes a light emitting unit 511, a lightemission controller 512, and a light receiving unit 513.

The light emitting unit 511 has a light source that emits light of apredetermined wavelength, and emits irradiation light whose brightnessperiodically changes, to an object. For example, the light emitting unit511 has a light emitting diode that emits infrared light having awavelength of 780 nm to 1000 nm as the light source, and emitsirradiation light in synchronization with a square-wave light emissioncontrol signal CLKp supplied from the light emission controller 512.

Note that the light emission control signal CLKp is not necessarily of asquare wave, but has to be a periodic signal. For example, the lightemission control signal CLKp may be a sine wave.

The light emission controller 512 supplies the light emission controlsignal CLKp to the light emitting unit 511 and the light receiving unit513, and controls the timing to emit irradiation light. The frequency ofthe light emission control signal CLKp is 20 megahertz (MHz), forexample. Note that the frequency of the light emission control signalCLKp is not necessarily 20 megahertz (MHz), and may be 5 megahertz (MHz)or the like.

The light receiving unit 513 receives light reflected from the object,calculates distance information for each pixel in accordance with thelight reception result, and generates and outputs a depth image in whichthe depth value corresponding to the distance to the object (subject) isstored as a pixel value.

A light receiving element 1 having the pixel structure of any of theabove described first through sixth example configuration is used as thelight receiving unit 513.

For example, the light receiving element 1 as the light receiving unit513 calculates distance information for each pixel, from the signalintensity corresponding to the charges that have been distributed to thefloating diffusion region FD1 or FD2 of each pixel 10 in the pixel arrayunit 21 on the basis of the light emission control signal CLKp. Notethat the number of taps of each pixel 10 may be four or the like asdescribed above.

As described above, a light receiving element 1 having the pixelstructure of any of the first through sixth example configurationsdescribed above can be incorporated as the light receiving unit 513 intothe ranging module 500 that calculates and outputs informationindicating the distance to the object by an indirect ToF method. Thus,the ranging characteristics of the ranging module 500 can be improved.

<15. Example Configuration of an Electronic Apparatus>

Note that a light receiving element 1 can be applied to a ranging moduleas described above, and can also be applied to various electronicapparatuses such as an imaging device like a digital still camera or adigital video camera having a ranging function, and a smartphone havinga ranging function, for example.

FIG. 23 is a block diagram showing an example configuration of asmartphone as an electronic apparatus to which the present technology isapplied.

As shown in FIG. 23, a smartphone 601 includes a ranging module 602, animaging device 603, a display 604, a speaker 605, a microphone 606, acommunication module 607, a sensor unit 608, a touch panel 609, and acontrol unit 610, which are connected via a bus 611. Further, in thecontrol unit 610, a CPU executes a program, to achieve functions as anapplication processing unit 621 and an operation system processing unit622.

The ranging module 500 IN FIG. 22 is applied to the ranging module 602.For example, the ranging module 602 is disposed in the front surface ofthe smartphone 601, and performs ranging for the user of the smartphone601, to output the depth value of the surface shape of the user's face,hand, finger, or the like as a measurement result.

The imaging device 603 is disposed in the front surface of thesmartphone 601, and acquires an image showing the user by performingimaging of the user of the smartphone 601 as the subject. Note that,although not illustrated, the imaging device 603 may also be disposed inthe back surface of the smartphone 601.

The display 604 displays an operation screen for performing processingwith the application processing unit 621 and the operation systemprocessing unit 622, an image captured by the imaging device 603, or thelike.

The speaker 605 and the microphone 606 output the voice from the otherend, and collect the voice of the user, when a voice call is made withthe smartphone 601, for example.

The communication module 607 performs network communication via acommunication network such as the Internet, a public telephone network,a wide area communication network for wireless mobile objects, such as aso-called 4G network or a 5G network, a wide area network (WAN), or alocal area network (LAN), short-range wireless communication such asBluetooth (registered trademark) or near field communication (NFC), orthe like. The sensor unit 608 senses velocity, acceleration, proximity,and the like, and the touch panel 609 acquires a touch operationperformed by the user on an operation screen displayed on the display604.

The application processing unit 621 performs processing for providingvarious services through the smartphone 601. For example, theapplication processing unit 621 can perform a process of creating a faceby computer graphics that virtually reproduces the user's expression anddisplaying the face on the display 604, on the basis of the depth valuesupplied from the ranging module 602.

The application processing unit 621 can also perform a process ofcreating three-dimensional shape data of a three-dimensional object, forexample, on the basis of the depth value supplied from the rangingmodule 602.

The operation system processing unit 622 performs a process to achievethe basic functions and operations of the smartphone 601. For example,the operation system processing unit 622 can perform a process ofauthenticating the user's face on the basis of the depth value suppliedfrom the ranging module 602, and releasing the lock on the smartphone601. Further, the operation system processing unit 622 performs aprocess of recognizing a gesture of the user on the basis of the depthvalue supplied from the ranging module 602, and then performs a processof inputting various operations in accordance with the gesture, forexample.

In the smartphone 601 configured as above, the ranging module 500described above is used as the ranging module 602, so that the distanceto a predetermined object can be measured and displayed, orthree-dimensional shape data of the predetermined object can be createdand displayed, for example.

<16. Example Applications to Moving Objects>

The technology according to the present disclosure (the presenttechnology) can be applied to various products. For example, thetechnology according to the present disclosure may be embodied as anapparatus mounted on any type of moving object, such as an automobile,an electrical vehicle, a hybrid electrical vehicle, a motorcycle, abicycle, a personal mobility device, an airplane, a drone, a vessel, ora robot.

FIG. 24 is a block diagram schematically showing an exampleconfiguration of a vehicle control system that is an example of a movingobject control system to which the technology according to the presentdisclosure can be applied.

A vehicle control system 12000 includes a plurality of electroniccontrol units connected via a communication network 12001. In theexample shown in FIG. 24, the vehicle control system 12000 includes adrive system control unit 12010, a body system control unit 12020, anexternal information detection unit 12030, an in-vehicle informationdetection unit 12040, and an overall control unit 12050. A microcomputer12051, a sound/image output unit 12052, and an in-vehicle networkinterface (I/F) 12053 are also shown as the functional components of theoverall control unit 12050.

The drive system control unit 12010 controls operations of the devicesrelated to the drive system of the vehicle according to variousprograms. For example, the drive system control unit 12010 functions ascontrol devices such as a driving force generation device for generatinga driving force of the vehicle such as an internal combustion engine ora driving motor, a driving force transmission mechanism for transmittingthe driving force to the wheels, a steering mechanism for adjusting thesteering angle of the vehicle, and a braking device for generating abraking force of the vehicle.

The body system control unit 12020 controls operations of the variousdevices mounted on the vehicle body according to various programs. Forexample, the body system control unit 12020 functions as a keyless entrysystem, a smart key system, a power window device, or a control devicefor various lamps such as a headlamp, a backup lamp, a brake lamp, aturn signal lamp, a fog lamp, or the like. In this case, the body systemcontrol unit 12020 can receive radio waves transmitted from a portabledevice that substitutes for a key, or signals from various switches. Thebody system control unit 12020 receives inputs of these radio waves orsignals, and controls the door lock device, the power window device, thelamps, and the like of the vehicle.

The external information detection unit 12030 detects informationoutside the vehicle equipped with the vehicle control system 12000. Forexample, an imaging unit 12031 is connected to the external informationdetection unit 12030. The external information detection unit 12030causes the imaging unit 12031 to capture an image of the outside of thevehicle, and receives the captured image.

In accordance with the received image, the external informationdetection unit 12030 may perform an object detection process fordetecting a person, a vehicle, an obstacle, a sign, characters on theroad surface, or the like, or perform a distance detection process.

The imaging unit 12031 is an optical sensor that receives light, andoutputs an electrical signal corresponding to the amount of receivedlight. The imaging unit 12031 can output an electrical signal as animage, or output an electrical signal as distance measurementinformation. Further, the light to be received by the imaging unit 12031may be visible light, or may be invisible light such as infrared light.

The in-vehicle information detection unit 12040 detects informationabout the inside of the vehicle. For example, a driver state detector12041 that detects the state of the driver is connected to thein-vehicle information detection unit 12040. The driver state detector12041 includes a camera that captures an image of the driver, forexample, and, in accordance with detected information input from thedriver state detector 12041, the in-vehicle information detection unit12040 may calculate the degree of fatigue or the degree of concentrationof the driver, or determine whether the driver is dozing off.

In accordance with the external/internal information acquired by theexternal information detection unit 12030 or the in-vehicle informationdetection unit 12040, the microcomputer 12051 can calculate the controltarget value of the driving force generation device, the steeringmechanism, or the braking device, and output a control command to thedrive system control unit 12010. For example, the microcomputer 12051can perform cooperative control to achieve the functions of an advanceddriver assistance system (ADAS), including vehicle collision avoidanceor impact mitigation, follow-up running based on the distance betweenvehicles, vehicle speed maintenance running, vehicle collision warning,vehicle lane deviation warning, or the like.

The microcomputer 12051 can also perform cooperative control to conductautomatic driving or the like for autonomously running not depending onthe operation of the driver, by controlling the driving force generationdevice, the steering mechanism, the braking device, or the like inaccordance with information about the surroundings of the vehicle, theinformation having being acquired by the external information detectionunit 12030 or the in-vehicle information detection unit 12040.

The microcomputer 12051 can also output a control command to the bodysystem control unit 12020, in accordance with the external informationacquired by the external information detection unit 12030. For example,the microcomputer 12051 controls the headlamp in accordance with theposition of the leading vehicle or the oncoming vehicle detected by theexternal information detection unit 12030, and performs cooperativecontrol to achieve an anti-glare effect by switching from a high beam toa low beam, or the like.

The sound/image output unit 12052 transmits an audio output signaland/or an image output signal to an output device that is capable ofvisually or audibly notifying the passenger(s) of the vehicle or theoutside of the vehicle of information. In the example shown in FIG. 24,an audio speaker 12061, a display unit 12062, and an instrument panel12063 are shown as output devices. The display unit 12062 may include anon-board display and/or a head-up display, for example.

FIG. 25 is a diagram showing an example of installation positions ofimaging units 12031.

In FIG. 25, a vehicle 12100 includes imaging units 12101, 12102, 12103,12104, and 12105 as the imaging units 12031.

Imaging units 12101, 12102, 12103, 12104, and 12105 are provided at thefollowing positions: the front end edge of a vehicle 12100, a sidemirror, the rear bumper, a rear door, and an upper portion of the frontwindshield inside the vehicle, for example. The imaging unit 12101provided on the front end edge and the imaging unit 12105 provided onthe upper portion of the front windshield inside the vehicle mainlycapture images ahead of the vehicle 12100. The imaging units 12102 and12103 provided on the side mirrors mainly capture images on the sides ofthe vehicle 12100. The imaging unit 12104 provided on the rear bumper ora rear door mainly captures images behind the vehicle 12100. The frontimages acquired by the imaging units 12101 and 12105 are mainly used fordetection of a vehicle running in front of the vehicle 12100, apedestrian, an obstacle, a traffic signal, a traffic sign, a lane, orthe like.

Note that FIG. 25 shows an example of the imaging ranges of the imagingunits 12101 through 12104. An imaging range 12111 indicates the imagingrange of the imaging unit 12101 provided on the front end edge, imagingranges 12112 and 12113 indicate the imaging ranges of the imaging units12102 and 12103 provided on the respective side mirrors, and an imagingrange 12114 indicates the imaging range of the imaging unit 12104provided on the rear bumper or a rear door. For example, image datacaptured by the imaging units 12101 through 12104 are superimposed onone another, so that an overhead image of the vehicle 12100 viewed fromabove is obtained.

At least one of the imaging units 12101 through 12104 may have afunction of acquiring distance information. For example, at least one ofthe imaging units 12101 through 12104 may be a stereo camera including aplurality of imaging devices, or may be an imaging device having pixelsfor phase difference detection.

For example, in accordance with distance information obtained from theimaging units 12101 through 12104, the microcomputer 12051 calculatesthe distances to the respective three-dimensional objects within theimaging ranges 12111 through 12114, and temporal changes in thedistances (the speeds relative to the vehicle 12100). In this manner,the three-dimensional object that is the closest three-dimensionalobject on the traveling path of the vehicle 12100 and is traveling at apredetermined speed (0 km/h or higher, for example) in substantially thesame direction as the vehicle 12100 can be extracted as the vehiclerunning in front of the vehicle 12100.

Further, the microcomputer 12051 can set beforehand an inter-vehicledistance to be maintained in front of the vehicle running in front ofthe vehicle 12100, and can perform automatic brake control (includingfollow-up stop control), automatic acceleration control (includingfollow-up start control), and the like. In this manner, it is possibleto perform cooperative control to conduct automatic driving or the liketo autonomously travel not depending on the operation of the driver.

For example, in accordance with the distance information obtained fromthe imaging units 12101 through 12104, the microcomputer 12051 canextract three-dimensional object data concerning three-dimensionalobjects under the categories of two-wheeled vehicles, regular vehicles,large vehicles, pedestrians, utility poles, and the like, and use thethree-dimensional object data in automatically avoiding obstacles. Forexample, the microcomputer 12051 classifies the obstacles in thevicinity of the vehicle 12100 into obstacles visible to the driver ofthe vehicle 12100 and obstacles difficult to visually recognize. Themicrocomputer 12051 then determines collision risks indicating the risksof collision with the respective obstacles. If a collision risk is equalto or higher than a set value, and there is a possibility of collision,the microcomputer 12051 outputs a warning to the driver via the audiospeaker 12061 and the display unit 12062, or can perform driving supportfor avoiding collision by performing forced deceleration or avoidingsteering via the drive system control unit 12010.

At least one of the imaging units 12101 through 12104 may be an infraredcamera that detects infrared light. For example, the microcomputer 12051can recognize a pedestrian by determining whether or not a pedestrianexists in images captured by the imaging units 12101 through 12104. Suchpedestrian recognition is carried out through a process of extractingfeature points from the images captured by the imaging units 12101through 12104 serving as infrared cameras, and a process of performing apattern matching on the series of feature points indicating the outlinesof objects and determining whether or not there is a pedestrian, forexample. If the microcomputer 12051 determines that a pedestrian existsin the images captured by the imaging units 12101 through 12104, andrecognizes a pedestrian, the sound/image output unit 12052 controls thedisplay unit 12062 to display a rectangular contour line for emphasizingthe recognized pedestrian in a superimposed manner. The sound/imageoutput unit 12052 may also control the display unit 12062 to display anicon or the like indicating the pedestrian at a desired position.

An example of a vehicle control system to which the technology accordingto the present disclosure can be applied has been described above. Thetechnology according to the present disclosure can be applied to theexternal information detection unit 12030 and the imaging units 12031 inthe above described configuration.

Specifically, the light receiving element 1 or the ranging module 500can be applied to the distance detection processing block of theexternal information detection unit 12030 or the imaging unit 12031. Asthe technology according to the present disclosure is applied to theexternal information detection unit 12030 or the imaging unit 12031, thedistance to an object such as a person, a car, an obstacle, a signpost,or characters on a road surface can be measured with high accuracy. Withthe obtained distance information, it is possible to alleviate thedriver's fatigue, and enhance the safety of the driver and the vehicle.

Embodiments of the present technology are not limited to the abovedescribed embodiments, and various modifications can be made to themwithout departing from the scope of the present technology.

Further, in the light receiving element 1 described above, an example inwhich electrons are used as signal carriers has been described. However,holes generated through photoelectric conversion may also be used assignal carriers.

For example, it is possible to adopt a combination of all or some of theembodiments in the above described light receiving element 1.

Further, the advantageous effects described in this specification aremerely examples, and the advantageous effects of the present technologyare not limited to them and may include other effects.

Note that the present technology may also be embodied in theconfigurations described below.

(1)

A light receiving element including:

an on-chip lens;

a wiring layer; and

a semiconductor layer disposed between the on-chip lens and the wiringlayer,

in which the semiconductor layer includes: a photodiode;

a first transfer transistor that transfers electric charge generated inthe photodiode to a first charge storage portion;

a second transfer transistor that transfers electric charge generated inthe photodiode to a second charge storage portion; and

an interpixel separation portion that separates the semiconductor layersof adjacent pixels from each other, for at least part of thesemiconductor layer in the depth direction,

the wiring layer has at least one layer including a light blockingmember, and

the light blocking member is disposed to overlap with the photodiode ina plan view.

(2)

The light receiving element according to (1),

in which the interpixel separation portion penetrates the semiconductorlayer in the depth direction.

(3)

The light receiving element according to (1) or (2),

in which the semiconductor layer further includes:

a first additional capacitor;

a first switch transistor that connects the first additional capacitorto the first charge storage portion; a second additional capacitor; and

a second switch transistor that connects the second additional capacitorto the second charge storage portion.

(4)

The light receiving element according to (3),

in which the first additional capacitor and the second additionalcapacitor include a wiring capacitor of the wiring layer.

(5)

The light receiving element according to (4),

in which the wiring layer includes a layer in which the light blockingmember is formed, and a layer in which the wiring capacitor is formed,and

the wiring capacitor is formed in a layer farther from the semiconductorlayer than the light blocking member.

(6)

The light receiving element according to any one of (1) to (5),

in which the light blocking member includes two layers.

(7)

The light receiving element according to any one of (1) to (6), furtherincluding

an interpixel light blocking film at a pixel boundary portion of thesemiconductor layer.

(8)

The light receiving element according to any one of (1) to (7),

in which a region of the semiconductor layer located above thephotodiode is a moth-eye structure in which minute concavities andconvexities are formed.

(9)

The light receiving element according to any one of (1) to (8),

in which the semiconductor layer is formed with a second semiconductorlayer and the wiring layer that are bonded to each other, the secondsemiconductor layer being another semiconductor layer, and

the second semiconductor layer includes at least an amplificationtransistor and a selection transistor.

(10)

A ranging module including:

a light receiving member;

a light source that emits irradiation light having periodically varyingbrightness; and

a light emission controller that controls timing to emit the irradiationlight,

in which the light receiving element includes:

an on-chip lens;

a wiring layer; and

a semiconductor layer disposed between the on-chip lens and the wiringlayer,

the semiconductor layer includes:

a photodiode;

a first transfer transistor that transfers electric charge generated inthe photodiode to a first charge storage portion;

a second transfer transistor that transfers electric charge generated inthe photodiode to a second charge storage portion; and

an interpixel separation portion that separates the semiconductor layersof adjacent pixels from each other, for at least part of thesemiconductor layer in the depth direction,

the wiring layer has at least one layer including a light blockingmember, and

the light blocking member is disposed to overlap with the photodiode ina plan view.

(11)

An electronic apparatus including:

a ranging module including:

a light receiving member;

a light source that emits irradiation light having periodically varyingbrightness; and

a light emission controller that controls timing to emit the irradiationlight,

in which the light receiving element includes: an on-chip lens;

a wiring layer; and

a semiconductor layer disposed between the on-chip lens and the wiringlayer,

the semiconductor layer includes:

a photodiode;

a first transfer transistor that transfers electric charge generated inthe photodiode to a first charge storage portion;

a second transfer transistor that transfers electric charge generated inthe photodiode to a second charge storage portion; and

an interpixel separation portion that separates the semiconductor layersof adjacent pixels from each other, for at least part of thesemiconductor layer in the depth direction,

the wiring layer has at least one layer including a light blockingmember, and

the light blocking member is disposed to overlap with the photodiode ina plan view.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

REFERENCE SIGNS LIST

1 Light receiving element

10 Pixel

PD Photodiode

RST Reset transistor

SEL Selection transistor

TRG Transfer transistor

FD Floating diffusion region

FDG Switch transistor

FDL Additional capacitor

M Metal film

MEM Memory

OFG Charge ejection transistor

21 Pixel array unit

41 Semiconductor substrate (first substrate)

42 Multilayer wiring layer

43 Antireflective film

44 Pixel boundary portion (boundary portion)

45 Interpixel light blocking film

47 On-chip lens

61 Interpixel separation portion

63 Light blocking member (reflective member)

64 Wiring capacitor

211 Interpixel separation portion

221 Antireflective film

223 PD upper region

301 Semiconductor substrate (second substrate)

321 Multilayer wiring layer

500 Ranging module

511 Light emitting unit

512 Light emission controller

513 Light receiving unit

601 Smartphone

602 Ranging module

What is claimed is:
 1. A light receiving element comprising: aphotodiode disposed in a semiconductor layer, the semiconductor layerdisposed between an on-chip lens and a multi wiring layer in across-sectional view: a first transfer transistor that transferselectric charge generated in the photodiode to a first memory; a secondtransfer transistor that transfers electric charge accumulated in thefirst memory to a first floating diffusion region; a third transfertransistor that transfers electric charge generated in the photodiode toa second memory; and a fourth transfer transistor that transferselectric charge accumulated in the second memory to a second floatingdiffusion region, wherein the photodiode, a gate electrode of the firsttransfer transistor, and the first memory are arranged along a firstdirection in a plan view, wherein the first memory, a gate electrode ofthe second transfer transistor, and the first floating diffusion regionare arranged along a second direction in the plan view, and wherein thesecond direction is different from the first direction.
 2. The lightreceiving element according to claim 1, further comprising: a resettransistor configured to reset a potential of the first floatingdiffusion region; and wherein a gate electrode of the reset transistoris arranged along the second direction in the plan view.
 3. The lightreceiving element according to claim 2, further comprising: anamplification transistor coupled to the floating diffusion region; and aselection transistor coupled to the amplification transistor, wherein agate electrode of the amplification transistor and a gate electrode ofthe selection transistor are arranged along the second direction in theplan view.
 4. The light receiving element according to claim 1, whereinthe photodiode, a gate electrode of the third transfer transistor, andthe second memory are arranged along a third direction in the plan view,and wherein the third direction is different from the first direction.5. The light receiving element according to claim 1, wherein the secondmemory, a gate electrode of the fourth transistor, and the secondfloating diffusion region are arranged along a fourth direction in theplan view, and wherein the fourth direction is different from the seconddirection.
 6. The light receiving element according to claim 1, furthercomprising: a fifth transfer transistor that transfers electric chargegenerated in the photodiode to a third memory; a sixth transfertransistor that transfers electric charge accumulated in the thirdmemory to a third floating diffusion region; a seventh transfertransistor that transfers electric charge generated in the photodiode toa fourth memory; and an eighth transfer transistor that transferselectric charge accumulated in the fourth memory to a fourth floatingdiffusion region.
 7. The light receiving element according to claim 6,wherein third memory, a gate electrode of the fifth transfer transistor,and the photodiode are arranged along the first direction in the planview.
 8. The light receiving element according to claim 7, wherein thethird memory, a gate electrode of the sixth transfer transistor, and thethird floating diffusion region are arranged along the fifth directionin the plan view, and wherein the fifth direction is different from thefirst direction.
 9. The light receiving element according to claim 6,wherein the photodiode is disposed between a gate electrode of firsttransfer transistor and a gate electrode of the fifth transfertransistor in the plan view.
 10. The light receiving element accordingto claim 6, wherein the photodiode is disposed between a gate electrodeof third transfer transistor and a gate electrode of the seventhtransfer transistor in the plan view.
 11. An electronic apparatuscomprising an application processing unit, a light emitting unit, andthe light receiving element according to claim 1, wherein the lightemitting unit is configured to emit light to an object, wherein thelight receiving element is configured to receive light reflected by theobject and output a data according to a distance to the object, andwherein the application processing unit is configured to performprocessing according to the data